This invention related to the coating of inorganic substrates such as glass with thin, non-iridescent coatings. Such coatings may consist primarily of fluorine-doped tin oxide of high reflectivity, especially to far infra-red radiation and the heat carried by such radiation.
The presently-known art to which this invention most closely relates is found in U.S. Pat. Nos. 4,146,657; 4,187,336; and 4,206,252. The most pertinent of these patents is U.S. Pat. No. 4,206,252, issued on June 3, 1980.
The teachings of these three patents is incorporated by reference in the present application. In general, U.S. Pat. No. 4,146,657 disclosed a particularly valuable tin oxide coating material and a novel process for depositing the coating. It was next found that this improved coating was so effective with respect to its electrical and infra-red reflecting properties that it could be utilized on architectural glass at very low thicknesses (e.g., from 0.1 to 0.8 microns). Some undesirable iridescent effects were present at such thicknesses. U.S. Pat. No. 4,187,336 disclosed improved processes and products whereby these iridescent effects were largely eliminated by use of thin intermediate coatings which were of selected refractive indices and were positioned over the substrate, e.g. glass, and under the infra-red reflective coating. Finally, U.S. Pat. No. 4,206,252 disclosed an improved process whereby the intermediate coating could be applied as a gradient coating on a continuous production line such as those lines used in commercial sheet-glass manufacture, e.g. float-glass production lines.
In the process of U.S. Pat. No. 4,206,252 a gaseous mixture of reactants was fed to a reaction zone through which the hot substrate was moving. The mixture was chosen so that some reactants reacted and deposited on the substrate faster than others. Thus, as the substrate moved along, it encountered an infinite series of constantly-changing coating compositions. The result was that the coated glass product picked up a coating with, ideally, a constantly changing intermediate layer between the substrate and the conductive tin oxide coating.
The method utilized in the U.S. Pat. No. 4,206,252 coating process required substantial care and attention to adequately maintaining gas seals at the reaction zone through which the hot glass passed. The present invention derives from applicant's efforts to minimize the sealing problem in continuous-coating apparatus. As will be seen below, the resulting novel process not only solves the sealing problem, but also provides an excellent, anti-iridescent, coated glass product of novel construction. It is to be understood that the term "seal" as used herein does not define an extremely tight seal, but merely refers to practical means to minimize the loss of gaseous material from the reaction zone, and thereby redirect it to primary apparatus venting means.